9-3a=-3(a-3)
a²-9=(a+3)(a-3)
分母(9-3a)与(a²-9)的最简公分母是3(a+3)(a-3)
2/(9-3a)=2/[-3(a-3)]
=-2/[3(a-3)]
=-[2(a+3)]/[3(a+3)(a-3)]
(a-1)/(a²-9)=(a-1)/[(a+3)(a-3)]
=[3(a-1)]/[3(a+3)(a-3)]
9-3a=-3(a-3)
a²-9=(a+3)(a-3)
分母(9-3a)与(a²-9)的最简公分母是3(a+3)(a-3)
2/(9-3a)=2/[-3(a-3)]
=-2/[3(a-3)]
=-[2(a+3)]/[3(a+3)(a-3)]
(a-1)/(a²-9)=(a-1)/[(a+3)(a-3)]
=[3(a-1)]/[3(a+3)(a-3)]